24.2 Extending Python Without Python s C API

24.2 Extending Python Without Python's C API

You can code Python extensions in other classic compiled languages besides C. For Fortran, the choice is between Paul Dubois's Pyfort (available at http://pyfortran.sf.net) and Pearu Peterson's F2PY (available at http://cens.ioc.ee/projects/f2py2e/). Both packages support and require the Numeric package covered in Chapter 15, since numeric processing is Fortran's typical application area.

For C++, the choice is between Gordon McMillan's simple, lightweight SCXX (available at http://www.mcmillan-inc.com/scxx.html), which uses no templates and is thus suitable for older C++ compilers, Paul Dubois's CXX (available at http://cxx.sf.net), and David Abrahams's Boost Python Library (available at http://www.boost.org/libs/python/doc). Boost is a package of C++ libraries of uniformly high quality for compilers that support templates well, and includes the Boost Python component. Paul Dubois, CXX's author, recommends considering Boost. You may also choose to use Python's C API from your C++ code, using C++ in this respect as if it was C, and foregoing the extra convenience that C++ affords. However, if you're already using C++ rather than C anyway, then using SCXX, CXX, or Boost can substantially improve your programming productivity when compared to using Python's C API.

If your Python extension is basically a wrapper over an existing C or C++ library (as many are), consider SWIG, the Simplified Wrapper and Interface Generator (available at http://www.swig.org). SWIG generates the C source code for your extension based on the library's header files, generally with some help in terms of further annotations in an interface description file.

Greg Ewing is developing a language, Pyrex, specifically for coding Python extensions. Pyrex (found at http://www.cosc.canterbury.ac.nz/~greg/python/Pyrex/) is an interesting mix of Python and C concepts, and is already quite usable despite being a new development.

The weave package (available at http://www.scipy.org/site_content/weave), lets you run inline C/C++ code within Python. The blitz function, in particular, generates and runs C++ code from expressions using the Numeric package, and thus requires Numeric.

If your application runs only on Windows, the most practical way to extend and embed Python is generally through COM. In particular, COM is by far the best way to use Visual Basic modules (packaged as ActiveX classes) from Python. COM is also the best way to make Python-coded functionality (packaged as COM servers) available to Visual Basic programs. The standard Python distribution for Windows does not directly support COM: you also need to download and install the platform-specific win32all extension package (available at http://starship.python.net/crew/mhammond/). I do not cover Windows-specific functionality, including COM, any further in this book. For excellent coverage of platform-specific Python use on Windows, I recommend Python Programming on Win32, by Mark Hammond and Andy Robinson (O'Reilly).